Genes involved in the determination of segmental identity in Drosophila melanogaster have been identified on the basis of genetic interactions with homeotic mutations, mutations already known to affect the process. Mutations in previously-identified homeotic genes have been recovered, as well as mutations in new homeotic genes. Several of the new homeotic genes have been characterized in more detail. Mutants for the moira gene have a phenotype that is very similar, if not identical, to the phenotypes of mutants in two other homeotic genes, the trithorax and ash-1 genes. All three genes appear to regulate the same target genes; the common target genes include Ultrabithorax, Sex combs reduced, and engrailed. The kismet gene, a post-transcriptional regulator of the Antennapedia gene, spans >70 kb of genomic DNA and encodes two partially-overlapping transcripts (8 and 17 kb in length). Maternally-expressed transcripts are distributed uniformly throughout the embryo, but disappear rapidly after the early stages of embryogenesis. Late in embryogenesis, zygotic expression of both transcripts appears to be almost exclusively confined to the nervous system. The brahma gene encodes a single 5.5 kb transcript that is expressed in similar temporal and spatial patterns to the patterns of kismet expression. Brahma is an activator of homeotic genes in Drosophila, and protein sequence similarities between brahma and the yeast transcriptional activator SNF2 suggest that brahma functions as part of a complex of proteins that activates transcription of target genes. One of the conserved regions between the brahma and SNF2 protein sequences is also conserved among a number of other proteins (the yeast SPT7, the Drosophila fsh, and the human CCG1 proteins). Except for CCG1, all of these proteins have been shown to function as activators of other genes, suggesting a functional role for the conserved domain.